In the conventional phone system, when a phone line is out-of-service, the phone line is completely dead. In other words, the phone line has no loop current and generates no sound. The same remains true if the telephone line is broken. Thus, the user of a telephone line has no ability to determine the difference between these two possibilities, and therefore must act to determine which one is the case. With the arrival of Internet Protocol (IP) Telephony, there is an opportunity to improve upon the Public Switched Telephone Network (PSTN) model.
Thus, the present invention is therefore directed to the problem of developing a method and apparatus for distinguishing between an out-of-service telephone line and a broken telephone line in Internet Protocol Telephony.